Separation of Pd and Pt from highly acidic leach liquor of spent automobile catalysts with monothio-Cyanex 272 and trioctylamine

Platinum group metals (PGMs), especially Pd, Pt, and Rh, have drawn great attention due to their unique features. Direct separation of Pd and Pt from highly acidic automobile catalyst leach liquors is disturbed by various factors. This work investigates the effect of various parameters including the acidity, extractant concentration, phase ratio A/O, and diluents on the Pd and Pt extraction and their stripping behaviors. The results show that the Pd and Pt are successfully separated from simulated leach liquor of spent automobile catalysts with monothio-Cyanex 272 and trioctylamine (TOA). Monothio-Cyanex 272 shows strong extractability and specific selectivity for Pd, and only one single stage is needed to recover more than 99.9% of Pd, leaving behind all the Pt, Rh, and base metals of Fe, Mg, Ce, Ni, Cu, and Co in the raffinate. The loaded Pd is efficiently stripped by acidic thiourea solutions. TOA shows strong extractability for Pt and Fe at acidity of 6 mol·L^–1 HCl. More than 99.9% of Pt and all of the Fe are extracted into the organic phase after two stages of countercurrent extraction. Diluted HCl easily scrubs the loaded base metals (Fe, Cu, and Co). The loaded Pt is efficiently stripped by 1.0 mol·L^–1 thiourea and 0.05–0.1 mol·L^–1 NaOH solutions. Monothio-Cyanex 272 and TOA can realize the separation of Pd and Pt from highly acidic leach liquor of spent automobile catalysts.